The amount of information and content available on the Internet continues to grow very fast. Given the vast amount of information, search engines have been developed to facilitate searching for electronic documents. In particular, users may search for information and documents by entering search queries comprising one or more terms that may be of interest to the user. After receiving a search query from a user, a search engine identifies documents and/or web pages that are relevant based on the search query. Because of its utility, web searching, that is, the process of finding relevant web pages and documents for user issued search queries has arguably become the most popular service on the Internet today.
Search engines operate by crawling documents and indexing information regarding the documents in a search index. When a search query is received, the search engine employs the search index to identify documents relevant to the search query. For instance, a ranking function may be employed to determine the most relevant documents to present to a user based on a search query. Ranking functions, however, have become increasingly complex such that hundreds of features are used to rank documents. Complex ranking functions, when used alone, are ineffective because of cost and time constraints.